Continuous sheet graining process

ABSTRACT

This invention relates to the graining of metal sheet especially of the type employed as the supporting base for lithographic printing plates. More particularly, this invention relates to the continuous ball graining of such metal sheet and processes for effecting such continuous ball graining.

United States Patent Testolill [451 Oct. 31, 1972 CONTINUOUS SHEET GRAINING [56] References Cited PROCESS [72] Inventor: Reno J. Testolin, Wheaton, lll. UNTED STATES PATENTS 73 A 2 Th m 2,311,047 2/1943 Hagelin ..51/6 ux 1 Sslgnee r 3' Cmpmy Melmse 2,448,316 8/1948 Lesavoy ..51/317 x 2,458,108 1/1949 Simpson ..;.51/6 2] Filed: Dec. 13, 1971 2,457,453 12/1948 Dunn", ..51/6 [21 Appl' 207 334,209 1/1886 Wooster ..51/20 Related US Application Dam Primary Examiner-Dona ld G. Kelly Att0meyJohn L. Hutchmson et al. 1 D Y 2l3q .9.2725. Ma 16, 1970,

This invention relates to the graining of metal sheet [52] US. Cl. ..51/317, 51/323, 51/292 especially of the type employed as the supporting base [51] Ill!- Cl. "B241? 31/06 for lithographic printing plates More particularly, this [5 8] held of invention relates to the continuous ball graining of such metal sheet and processes for effecting such continuous ball graining.

12 Claims, 7 Drawing Figures CONTINUOUS SHEET GRAINING PROCESS This is a Division of application Ser. No. 019,794, filed Mar. 16, 1970 now US. Pat. No. 3,643,379 issued Feb. 22, 1972.

The composite plates employed in lithographic printing typically comprise a supporting metal base or sheet having an intermediate hydrophillic coating and a final outer, over-layer of a light sensitive material such as a diazo resin. In the preparation of these plates, the supporting base metal sheet typically of aluminum is first roughened or grained prior to the application of any coatings. This graining provides a structure of microscopic hills and valleys on the sheet surface which increases its water receptivity or hydrophillic nature. Such roughening or graining of the printing surface of the metal sheet is carried out according to several different conventional procedures. One of the most common involves a ball graining procedure wherein the metal sheet is subject to the abrasive action of finely divided or particulate solids such as sand in the presence of metallic particles, for example, steel marbles. These metallic marbles or balls are maintained in an agitated state and force the abrasive against the surface of the metal sheet thereby effecting the desired graining of the metal sheet.

Conventionally, this ball graining operation is carried out in a batch-type procedure which involves basically placing a metal sheet on a vibratable, horizontal graining table, charging the metal marbles or balls and the finely divided abrasive, usually in an aqueous slurry, to

the graining table and onto the upper surface of the metal sheet and then vibrating the graining table to impart a rotary or oscillatory motion to the marbles positioned on the upper surface of the sheet for a period of time sufficient to achieve the desired degree of roughness or graining. While this batch-type procedure is widely employed, it nevertheless suffers from a number of undesirable features. Aside from the adverse economics of the batch operation, the roughened metal sheets produced have properties which vary widely from batch to batch. This results in a particularly undesirable inconsistency in printing performance when such metal sheets are ultimately employed as a supporting base for lithographic printing plates.

Accordingly, an object of this invention is to provide a process for continuously ball graining metal sheet particularly employable as the supporting base for lithographic printing plates. Another object is to provide such a continuous process which is economic and capable of producing grained metal sheets of uniform properties. A further object is to provide processes for effectively conducting such continuous ball graining. These and other objects of this invention will be apparent from the following further detailed description thereof as well as from the attached drawings.

IN THE DRAWINGS:

FIG. 1 is a diagrammatic view illustrating a continuous graining process according to this invention.

FIG. 2 is a perspective view of a graining table apparatus for effecting the continuous ball graining process of this invention.

FIG. 3 is a view in perspective of a graining table employable in the apparatus of FIG. 2 for practicing the process of this invention showing catching means for maintaining the graining marbles in fixed position thereon.

FIG. 4 is a sectional view along line 4-4 of FIG. 4 illustrating the graining table of FIG. 3 at an-angle a with the horizontal and with additional graining marbles.

FIG. 5 is an apparatus for practicing the process of this invention in perspective illustrating washing means combinable with the graining apparatus of FIG. 2.

FIG. 6 is a perspective view of another graining table employable in the apparatus of FIG. 2 for practicing the process of this invention having caging means with sections broken away.

FIG. 7 is a view along line 7-7 of FIG. 6 illustrating in cross-section a caging means confining the graining marbles.

In general reference to FIG. 1, the processof this invention for the continuous graining of metal sheet, in a simple embodiment, comprises charging a strip of metal sheet 10 to a graining zone illustrated by a graining table 11, contacting the upper surface of the sheet 10 with metallic particles such as graining balls 12 maintained in the presence of particulate abrasive 13, continuously charging fresh abrasive 13 to the graining zone and simultaneously withdrawing spent abrasive therefrom via conduits 14 and 15 respectively, maintaining the metal sheet 10 within the graining zone in contact with the abrasive l3 and metal balls 12 for a period of time sufficient to roughen at least the upper surface of the metal sheet 10 to the degree required for lithographic purposes, and thereafter continuously recovering the surface roughened metal sheet 10 from the graining zone. As illustrated in FIG. 1, the strip of metal sheet 10 in a preferred embodiment, is first passed to a washing zone illustrated as spray cabinet 16 and is contacted therein with high pressure water to remove any adhering abrasive prior to being recovered.

In specific reference to the process of this invention as generally illustrated in FIG. 1, the strip of metal sheet 10 is conveniently supplied to the graining table 11 of the graining zone from a wound coil or roll 17 of such metal sheet which turns in the arrow direction. The metal sheet 10 is suitably of a metal conventionally employed as a supporting base for composite lithographic plates. Typically such metal can include aluminum, its various alloys and oxides, zinc, tin, manganese, chrome, copper and various combinations and alloys thereof. Generally, however, the preferred metal is aluminum or its various alloys and oxides and conventionally the metal sheet is a relatively thin strip of aluminum having a thickness ranging from about 0.005

to about 0.030 inches and having a width from about 0.5 to about 6.0 feet.

As the coiled roll 17 of the metal sheet 10 is unwound and fed at a desired rate or linear velocity to the graining zone such as by means of carry roller 18, the upper surface of the metal sheet 10 comes into abrasive contact with the metal marbles or graining balls 12 and the particular abrasive l3 maintained within the graining zone. This graining zone can comprise any suitable device or apparatus which will permit the graining balls 12 to abrasively contact the upper surface of the metal sheet 10 with free rotating or gyrating motion in the presence of the particulate abrasive l3. advantageously and conveniently, the graining zone simply comprises a graining table 11, having a generally horizontally disposed working surface 19 over which the strip of metal sheet 10 continuously travels while the agitated, metallic particles such as the graining balls 12 are maintained in rotary movement upon the upper surface of the metal sheet 10. Several particularly suitable and preferred graining tables 11 for employment as the graining zone of this invention are hereinafter disclosed and more fully described.

The metallic particles which in agitated motion contact the upper surface of the metal sheet on the graining table 11 are preferably metal spheres such as the graining balls 12 which are capable of freely moving or rotating upon the surface of the metal sheet 10 to bring and force the particulate abrasive 13 against the surface and thereby cause the desired abrasive or graining action. Generally, metal balls of material such as surface hardened steel of the type commonly employed as ball bearings have the desired weight and surface hardness for use as metal particles in the graining zone. The size or diameter of these metal balls can be varied but usually for the graining of most types of metal sheet 10 employed for lithographic plates, the metal balls 12 have a diameter ranging from about 0.25 to about 0.5 inches. The quantity or number of metal balls in contact with the metal sheet having such diameters can be varied, but generally a sufficient number of the metal balls 12 are present within the graining zone so that they substantially cover, in one layer, the entire surface area of the sheet to be grained.

The inducement of agitation or movement to the metal balls 12 which causes their free rotation or gymtion upon the surface of the metal sheet 10 can be effected in different ways and several convenient and advantageous methods are hereinafter disclosed and described. Generally, however, the rotational movement of the metal balls 12 is conventionally created simply by vibrating or oscillating the-graining table 11 with an oscillator connected with the table so as to transfer such oscillating motion to the balls as positioned on the surface of the metal sheet. The degree of agitation or rotational movementof the metal balls 12 upon the upper surface of the metal sheet 10 is important in the obtainment of the desired degree of graining necessary for lithographic purposes. Because the movement of the metal graining balls 12 is in response to imparted motion, the degree of agitation can usually be described quantitatively by reference to the rotational speed of the mechanical device, such as the oscillator 20 which imparts the rotational movement to the metal balls 12. Usually, for most graining operations, the degree of agitation as measured by the rotation of an oscillating device should range from about 50 to about 250 revolutions per minute with a more limited range of from about 60 to 175 revolutions per minute generally being preferred.

The finely divided or particulate abrasive 13 which by the action of the rotating metal balls 12 roughens or grains the upper surface of the metal sheet 10 can include a large number of different materials. Generally, almost any of the finely divided, gritty materials conventionally employed to roughen or grind metals or their oxides can be employed. Suitable materials for this purpose include sand, pumice, marble, quartz, as well as various combinations and admixtures thereof. The particular particle size of the abrasive is important in achieving both the type and degree of graining desired for lithographic purposes. While the particle size of the abrasive can vary depending upon such factors as the type of metal being grained, the particular abrasive being employed and the degree of agitation of the metal balls, the average diameter of the abrasive particle generally should be maintained within from about 50 to about 175 microns, particularly for the graining of most metals such as aluminum.

So that the desired abrasive or graining action is achieved by the particulate abrasive 13 and the agitated metal balls 12, it generally is preferred that the abrasive particles be maintained at least partially in an aqueous slurry. The water, and preferably substantially mineral free water, in the slurry functions to continuously maintain the abrasive particles in close contact with the upper surface of the metal sheet 10 so as to maximize the abrasive action. It is also usually desirable to add a small proportion of a metal cleaning agent to the aqueous slurry so as to simultaneously achieve a cleaning of the metal surface during graining. This results in producing a grained surface substantially free of contamination which might interfere with any subsequent coating applied to the sheet. While the proportions of the solid abrasive in the slurry can bewidely varied, it usually is desirable to maintain a slurry heavy or highly concentrated with the solid abrasive. For most graining operations, the weight content of the abrasive slurry should be maintained within the range of from about to about weight percent abrasive. The amount of the metal cleaning agent present in the aqueous slurry as well as the particular agent employed will depend upon several factors including the type and quantity of surface contamination, for example, mill oils, present on the metal sheet as charged to the graining zone. Usually, however, with such agents as sodium phosphates particularly for aluminum sheet, the quantity present in the aqueous slurry can range from about 0.1 to about 1.0 weight percent. When the surface of the metal sheet 10 is excessively contaminated, for example, with mill oils, it may be desirable to preclean the surface of the metal sheet 10 prior to charging the metal sheet 10 to the graining zone. This may be accomplished by passing the strip of metal sheet 10 first through a degreasing zone as represented by bath 8 by means of the rollers 9. This bath 8 may suitably contain degreasing agents such as high boiling hydrocarbons or methylene dichloride to remove organic material as the strip of metal sheet 10 passes through the bath 8.

The abrasive action of the particulate abrasive 13 and metal balls 12 in addition to abrading or graining the upper surface of the metal sheet 10 also has the effect of breaking down or reducing the size of the individual abrasive particles. Accordingly, it is important that properly sized abrasive particles be continuously maintained within the graining zone to insure the desired graining action. This may be accomplished in several different ways, but most simply, involves continuously charging fresh abrasive having the desired size to the graining zone and withdrawing spent abrasive from the zone containing the abrasive particles reduced in size. The rate at which the fresh abrasive is charged to the graining zone will, of course, be dependent upon several factors and basically upon the rate at which the particle size is reduced by abrasive action within the graining zone. This in turn is a function of the type of abrasive used, its initial particle size, type of metal being grained, the degree'of graining desired, the

degree of agitation for the graining balls 12 as well as the rate at which the strip of metal sheet travels through the graining zone. Generally, however, for most operations, graining, for example, aluminum sheet, to the degree suitable for lithographic plate purposes and employing sand as the abrasive, the abrasive should be charged and withdrawn to the graining zone, under steady state conditions, at a rate of about 0.15 to 1.0 and preferably 0.4 to 0.6 pounds of abrasive per minute per square foot of metal sheet surface being grained.

In charging the abrasive 13 to the graining zone, it generally is preferred, according to one embodiment of this invention, to charge the abrasive 13 at one end of the graining zone and withdraw it from the opposite end in countercurrent flow to the direction of the strip of metal sheet 10. This tends to maximize the desired graining and its uniformity and can be accomplished by several methods including gravitational flow or mechanical assists which continuously direct the aqueous abrasive slurry in a direction counter-current to the moving strip of metal sheet 10.

The operating conditions for the graining zone under which the abrasion of the upper surface of the metal sheet 10 is effected according to the process of this invention can be varied with the conditions such as temperature, feed rate of the metal sheet 10 to the zone and the degree of agitation for the graining balls 12 in any instance being selected so as to achieve the degree of graining desired. Normally, the graining may be conducted under ambient temperatures within the range of from about 10 to about 40C. The rate at which the strip of metal sheet 10 is charged to the graining zone is a function of the residence time or time that the metal sheet is maintained within the graining zone necessary to achieve the desired degree of graining. This in turn is dependent upon such factors as the type of metal being grained, for example, aluminum, the abrasive employed and its particle size and the degree of agitation for the metal balls 12. Typically, however, when graining metals such as aluminum with sand and with the metal balls 12 oscillated at from 100 to 150 revolutions per minute, the strip' of metal sheet 10 should be charged to the graining zone at a feed rate sufficient to provide a residence time of the metal sheet within the zone of from about 40 to about 200 and preferably from about 80 to about 160 square feet of metal sheet surface to be grained per hour. In any event, the rate at which the metal sheet 10 is charged to the graining zone should be adjusted in reference to the other graining conditions so that the sheet is grained to the degree necessary for use in lithographic plates. This-degree of graining is conveniently measured by the wetability of the grained surface and in general the wetability of the grained surface should be such that a drop of distilled water makes a contact angle of from about 0 to about 30 degrees with the grained surface.

As the strip of metal sheet 10 exits from the graining zone with its upper surface sufficiently roughened for lithographic purposes, it is wiped clean of the abrasive slurry in a suitable wiping operation. The metal sheet 10 may then be wound into a coil or roll 21 or first further processed by application of various surface coatings using conventional coating equipment. However, as previously indicated, in a preferred embodiment, the strip of metal sheet 10 as it exits the graining zone and prior to being recovered is first passed to a washing zone as represented by spray cabinet 16 by means of carry roller 22. The strip of metal sheet 20 is contacted within the washing zone with high pressure water sprays which dislodge any adhering or embedded abrasive not removed by the wiping action as the metal sheet 10 exits the graining zone. If desired, the removal of the embedded abrasive by action of the high pressure water spray may be assisted by simultaneously subjecting the sprayed surface to the wiping action of mechanically driven brushes. The rate at which the strip of metal sheet 10 is charged to the washing zone will under steady stateconditions usually equal the rate that the strip of metal sheet 10 exits the graining zone and the residence time of the strip of metal sheet 10 within the washing zone is adjusted so that the metal sheet is washed and brushed free of any embedded abrasive. After the excess surface water is removed in a suitable wiping operation, the strip of metal sheet having a clean, grained upper surface suitable for lithographic purposes is wound upon the roll 21.

As indicated, there are a number of apparatus which may be utilized in the practice of the process of this invention and specifically for the graining table utilized as the graining zone to bring the moving strip of metal sheet into abrasive contact with the particulate abrasive in the presence of the agitated metal particles. There are, however, certain preferred apparatus which may be advantageously employed and several are generally illustrated in FIGS. 2 to 7. Basically, these apparatus comprise feeding means for continuously supplying a strip of the metal sheet to a graining table; such graining table being adapted to support metallic particles and particulate abrasive on the working surface of the table and in abrasive contact with the upper surface of the metal sheet; holding means for maintaining the lower surface of the metal sheet against the working surface of the graining table during travel of the metal sheet over the graining table; oscillating means for imparting agitating movement to the metallic particles to cause graining of the upper surface of metal sheet by action of the abrasive; means for continuously chargingand withdrawing the abrasive from the graining table and recovery means for continuously removing the strip of grained metal sheet from the graining table.

In the operation of such apparatus and in general reference to FIG. 2, a strip of metal sheet 25 is continuously supplied by feeding means 26 to a graining table 27 which is adapted to support metal graining balls 12 and particulate abrasive 13 on the working surface 28 of the graining table 27 in contact with the upper surface of the moving metal sheet 25. Holding means such as guides 29 maintain the lower surface of the metal sheet 25 against the working surface 28 and as the metal sheet 25 passes over the graining table 27, the upper surface of the metal sheet 25 is roughened or grained by the particulate abrasive 13 through action of the graining balls 12 which are sustained in agitated movement by oscillator 30. A continuous supply of abrasive 13, for example, sand in an aqueous slurry, is maintained on the working surface 28 by charging fresh abrasive via the feed pipe 31 and withdrawing spent abrasive via drain pipe 32. When the strip of metal sheet 25 has been grained to the degree necessary for lithographic purposes during passage over the graining table 27, the strip of metal sheet 25 is continuously collected by recovery means 33.

Referring more specifically to FIG. 2, the strip of metal sheet 25, for example, an aluminum sheet having a width of from about 0.5 to about 6.0 feet and a thickness of from about 0.005 to about 0.03 inches, is unwound in the arrow direction from a feeder roll 34 comprising conveniently a coil of such metal sheet 25 and is fed via a carry roller 43 to the graining table 27. The coiled feeder roll 34 is centrally supported on a shaft 35 which is rotatably mounted in bearings 36. The bearings 36 are supported by parallel frame bar 37 which extend horizontally from and are integrally connected to the graining table 27. These frame bars 37 are vertically supported at their terminal portions by stationary legs 38 which are connected thereto by intermediate spring mounts 39 so as to allow the frame bars 37 to be freely vibratable.

The graining table 27 as simply shown in FIG. 2, comprises essentially a working surface 28 shown horizontally disposed of suitable constructed material which is joined to upward extending, longitudinal side walls 40 and transverse side walls 41 at lower portions thereof, such side walls 40 and 41 completely bordering and enclosing the working surface 28. Enclosed by such side walls 40 and 41 and confined upon the working surface 28 are a plurality of metal graining balls 12 and particulate abrasive 13, for example, sand. For purposes of clarity and convenience, both graining balls 12 and particulate abrasive 13 are shown in exaggerated size and distribution. In typical operation of the graining table 27, there are a number of graining balls 12 sufficient to substantially cover in one layer the entire working surface 28 without precluding relatively free rotation or movement of the metal balls. The abrasive 13 is conventionally present in an aqueous slurry which completely covers the working surface 28.

The dimensions of the graining table 27 in respect to width and length can be varied but its width, that is the length of the transverse side walls 41, should be at least sufficient to accommodate the strip of metal sheet 25 between the longitudinal side walls 40 and generally should for operational convenience, exceed the width of such strip of metal sheet 25. Stationary legs 42 support the graining table 27 and are suitably connected to the bottom of the working surface 28 by means of intermediate spring mounts 44 which permit the graining table 27 to be freely vibrated by the oscillator 30 and thereby cause the metal balls 12 to oscillate in a responsive rotary motion. This oscillator 30 of conventional design is integrally connected to the graining table 27, as generally shown in FIG. 2, conveniently to the bottom of the working surface 28 and is controllable to provide rotary motion to the graining table 27 over a wide range of revolutions per minute.

As indicated, the strip of metal sheet 25 is fed to the graining table 27 from the feeder roll 34 via carrier roller 43 which is rotatably mounted by bearings 45 supported by vertical supports 46 which are fixedly connected to the frame bars 37. Carry roller 43 may be either freely rotatable or power driven and the length of the vertical supports 46 can be adjusted by conventional screw means (not shown) so as to provide the desired tension for the metal sheet 25. As the strip of metal sheet 25 passes from the carry roller 43, it contacts the working surface 28 of the graining table 27 at the point where the metal sheet 25 passes through a guide 29 which forces and guides the lower or bottom surface of the metal sheet 25 against the working surface 28 of the graining table 27. Guide 29, in simple embodiment, comprises a fixed or rotatable rod 47 spaced above the working surface 28 a distance sufficient to allow the metal sheet 25 to pass below the rod 47 while being forced against the working surface 28. This guide 29, thus generally operates to preclude any of the metal graining balls 12 as well as any substantial quantity of the abrasive 13 from becoming lodged beneath the metal sheet 25 between the working surface 28 and the bottom surface of the metal sheet 25. The rod 47 is fixedly mounted directly on the working surface 28 by means of brackets 48 and is positioned transversely to the strip of metal sheet 25. While the length of the rod 47 can vary, it usually is of a length exceeding the width of the strip of metal sheet 25. Any number of similar guides 29 can be utilized along the path of the strip of metal sheet 25 as it travels over the working surface 28 of the graining table 27, with the particular number chosen in any instance being at least sufficient to maintain the bottom surface of the strip of metal sheet 25 substantially flush against the working surface 28. For simplicity, only two guides 29 and 29a are illustrated for the graining table 27 in FIG. 1 preferably disposed at opposite ends of such table.

As the strip of metal sheet 25 exits from the guide 29, the metal graining balls 12 and particularly abrasive 13, for example, sand or marble chips in an aqueous slurry, roll and flow upon the upper surface of the traveling strip of metal sheet 25. As previously indicated, the graining balls 12 are in agitated motion in response to the motion imparted to the working surface 28 by the oscillator 30 and this motion forces the abrasive 13 into abrasive contact with upper surface of the metal sheet 25 so as to grain such surface as the metal sheet 25 travels over the working surface 28 of the graining table 27 At the opposite end of the graining table 27 the metal sheet 25 passes through the second guide 29a prior to leaving the graining table 27 by passing upward and over a carry roller 49. This second guide 29a, as previously indicated, is of a construction similar to the guide 29 and comprises an elongated rod 50 mounted on brackets 51 which forces the lower surface of the metal sheet 25 against the working surface 28 as the metal sheet passes under the rod 50. The carry roller 49 is shown advantageously positioned at an elevation above the working surface 28 so as to raise the strip of metal sheet 25 and allow the guide 29a to wipe adhering abrasive 13 from the surface of the metal sheet 25 The graining balls 12 simply roll off the metal sheet 25 as it passes through the guide 29a. If the wiping action of the guide 29a is insufficient to remove all adhering abrasive, then such wiping action may be complemented by squeeze rolls or brushes (not shown). The carry roller 49 like carry roller 43 may be either power driven or freely rotatable and is mounted on bearings 52 which are supported by vertical supports 53 which in turn are fixedly connected to frame bars 54. The parallel frame bars 54 like frame bars 37 extend horizontally from and are integrally connected to the graining table 27 and each is vertically supported at its terminal portion by stationary leg 55 connected thereto by intermediate spring mounts 56. The length of the vertical supports 53 can be adjusted to provide variable tension for the metal sheet 25 as it passes over the carry roller 49.

Also located at the terminal portions of the frame bars 54 above the legs 55 are bearings 57 which rotatably support a shaft 58 internal to a collector roll 59. This collector roll 59 like the feeder roll 34 can be composed simply of a coil of the strip of metal sheet 25 and is formed by winding the strip of metal sheet 25 in the arrow direction about the shaft 58 as it leaves the carry roller 49. The collector roll 59 is rotatably driven by motor means 60 which are in driving communication with the shaft 58 through conventional pulley and gearing means (not shown). The motor means 60 are equipped with variable speed controls so that the collector roll 59 can be rotated over a wide range of rotational speeds. As the collector roll 59 is rotated by the motor means 60 in the arrow direction, the strip of metal sheet 25, as indicated in FIG. 2, is wound upon the collector roll 59 and this winding action serves to unwind the metal sheet 25 from the feeder roll 34 in the arrow direction and pull the metal sheet 25 across the working surface 28.

Both the bearings 36 and 57 and their associated mountings (not shown) are so adapted that both the feeder roll 34 and the collector roll 59 can be removed from the frame bars 37 and 54, respectively, and exchanged for a second set of similar shaft mounted rolls when either the feeder roll 34 has been completely unwound or the collector roll 59 completely wound with the desired quantity of metal sheet 25. Other conventional winding and unwinding equipment may be associated with the feeder and collector rolls 34 and 59 such as splicers, edge trimmers and cutters (not shown). The feeder roll assembly may also, if desired, be associated with a second unwind assembly (not shown) which would rotatably support a second feeder roll of the strip of metal sheet, for example, on extensions of the frame bars 37 so that when all of the metal sheet 25 has been unwound from the feeder roll 34, the end of the strip of the metal sheet 25 may be spliced to the start of another strip of metal sheet from the second feeder roll thereby allowing continuous operation of the graining table without any necessity for shutting down the graining operation when all of the metal sheet 25 has been unwound from the feeder roll 34.

With reference to one specific embodiment of the process of this invention for the apparatus of FIG. 2, because the feeder roll 34 and collector roll 59 as well as the carry rollers 43 and 49 are integrally connected to the graining table 27, for example, by means of the horizontal frame bars 37 and 54, the strip of metal sheet 25 will oscillate or vibrate as it winds and unwinds at the same rotational frequency of the graining table 27 as induced by the oscillator 30. This arrangement is particularly desirable in that there will be little or no stress applied to the strip of metal sheet 25 as it contacts and leaves the vibrating graining table 27 inasmuch as the metal sheet will be vibrating or oscillating at the same frequency. This will substantially preclude any undesirable flexing or twisting of the metal sheet 25 particularly along its longitudinal edges which might adversely affect the employment of the metal sheet, when grained, for lithographic purposes.

In the event that the graining operation due to the particular graining conditions employed does not cause excessive flexing or twisting of the edges of the metal sheet 25 when it contacts and leaves the graining table 27, then the feeder roll 34 and collector roll 59 need not be integrally connected to the graining table 27 such as by means of the horizontal frame bars 37 and 54. Under such circumstances, such frame bars need not be integrally connected to the bearings 36 and 57 for the feeder roll 34 and collector roll 59, respectively, and such bearings may be supported solely by the stationary legs 38 and 55, respectively.

So that the graining operation may be continuous, fresh particulate abrasive such as sand of the desired particle size may be charged conveniently in an aqueous slurry to the graining table 27 via the feed pipe 31 and spent abrasive containing abrasive of reduced particle size may be withdrawn from the graining table via drain pipe 32. The drain pipe 32 communicates with the working surface 28 and has suitable screening means (not shown) to preclude any loss of the metal balls 12. The effluent abrasive slurry from the drain pipe 32 can fall freely into a trough 61 from which the abrasive slurry may be withdrawn and after separation of the abrasive of undesired size recycled with fresh abrasive makeup to the feed pipe 31. It usually is desirable to charge and to withdraw the abrasive to the graining table 27 so that the general flow of abrasive slurry is in a direction countercurrent to the direction of the strip of metal sheet 25 as it moves over the working surface 28. This can be accomplished simply as shown in FIG. 2 by charging the abrasive via pipe 31 at the exit end of the graining table 27 and withdrawing spent abrasive via drain pipe 32 from the opposite end. This method may be complemented by disposing the graining table 27 at a slight angle with the horizontal of from 1 to 5 with the graining table being elevated at the exit end where the metal sheet 25 leaves the graining table 27. The abrasive slurry can then flow downward towards the drain pipe 32 at the opposite end. This arrangement is generally illustrated by FIGS. 3 and 4 showing a graining table 65 disposed at an angle a with the horizontal as well as several associated assemblies.

The graining table 65 of FIGS. 3 and 4 is analogous to the graining table 27 of FIG. 2 and is simply shown composed of a working surface 66, bordered by upward extending longitudinal and transverse side walls 67 and 68, respectively. Certain details of graining table 65 as shown for the graining table 27 of FIG. 2 are omitted for convenience. So that the metal graining balls 12 may be uniformly positioned upon the working surface 66 of the graining table 65 while the graining table is disposed at an angle a with the horizontal, various restraining means may be employed to hold the metal balls 12 in fixed position and thus preclude their rolling to the lower or charging end of the graining table 65. A suitable restraining means is illustrated in FIGS. 3 and 4 where a plurality of vertical catching plates 69 are shown extending transversely across the graining table 65. These catching plates 69 are joined at their terminals to the longitudinal sides 67 and their lower edges 70 are disposed a distance above the working surface 66 sufficient to allow free passage of the strip of metal sheet 25 in one direction and the abrasive in the opposite or downward direction. This distance of the catching plates 69 above the working surface 66 is not however sufficient to allow passage of the metal balls 12 between the lower edges 70 and either the moving strip of metal sheet 25 or the working surface 66. The catching plates 69 thus trap and hold the metal balls 12 in a fixed and desired position on the working surface 66. Various other means may also be employed independent of or in cooperation with the disposing of the graining table 65 at an angle a so as to direct the abrasive countercurrent to the moving strip of metal sheet 25. Such other means can include various mechanical assists such as brushes, paddles or pumps to direct the abrasive slurry from the feed pipe 31 at the exit end of the graining table 27 (FIG. 2) to the drain pipe 32 at the opposite end.

In reference to FIGS. 2 and 5, as the strip of metal sheet 25 exits the graining table 27, there still may be abrasive particles adhering or embedded in the grained surface of the metal sheet 25 which are not completely removed by the wiping action of the guide 29a or any associated squeeze rolls (not shown). Accordingly, in a preferred embodiment, the strip of metal sheet 25 is first passed through washing means 71 prior to being wound upon the collector roll 59 so as to completely remove any of the, adhering and embedded abrasive particles. As shown in FIG. 5, the washing means 71 comprises basically washer sprays 72 and a pan 73 where such pan is fixedly mounted by conventional securing means (not shown) between the frame bars 54 and positioned on such frame bars between the carry roller 49 and the collector roll 59 (FIG. 2). In operation of the washing means 71, the strip of metal sheet 25 passes from the carry roller 49 to and under a washer roller 74 rotatably supported by bearings 75 mounted on the pan 73 and then passes under the water sprayers 72 which direct high pressure water upon the grained surface of the metal sheet 25 to dislodge any embedded abrasive. If desired, the surface of the metal sheet may also be subjected to the action of brushes (not shown) to assist in removing embedded abrasive. After passing under the sprayers 72, the strip of metal sheet 25 then continues under a second washer roller 76 rotatably supported by bearings 77 mounted on the pan 73 and is then wound upon the collector roll 59. Any excessive water may be removed from the metal sheet 25, if desired, by first passing the strip of metal sheet 25 prior to being rewound upon the collector roll 59 through a series of squeeze rolls (not shown). The effluent water in the pan 73 is removed via an exit drain 78. Because the pan 73 and its associated washer rollers 74 and 76 are also integrally connected to the graining table 27 via the frame bars 54, the vibrations produced by oscillator 30 (FIG. 2) will also be transmitted from the graining table to the washing means 71 so that the metal sheet 25 will not be subjected to any undesirable stresses when passing from the carrier roller 49 to the washer roller 74 and from the washer roller 76 to the collector roller 59. So that the entire washing means 71 may be freely vibratable, the water to the sprays 72 via header pipe 79 may be delivered through a flexible hose 80 from a water source (not shown) and the header pipe 79 may be fixedly supported and integral with the pan by means of supports 81.

If desired, a degreasing device similar to the pan 73 of the washing means 71 may be employed to preclean the strip of metal sheet 25 prior to being charged to the graining table 27. This degreasing device is not illustrated but may be constructed in a fashion similar to the pan 73 of FIG. 5 and mounted between the frame bars 37 and positioned thereon between the carry roller 43 and the graining table 27 of FIG. 2. The pan of the degreasing device can contain a suitable degreasing solvent to remove surface contamination as the strip of metal sheet 25 passes through the solvent.

As illustrated generally for the graining table 27 of FIG. 2, the oscillatory motion for the metal balls 12 necessary to achieve the desired graining of the metal sheet 25, is imparted to the metal balls by oscillation of the entire graining table 27 by means of the oscillator 30. This oscillatory motion may also be imparted to the metal graining balls 12 by other suitable means and one such arrangement is illustrated in simple embodiment in FIGS. 6 and 7. Referring specifically to FIG. 6, a graining table is shown of construction analogous to the graining table 27 of FIG. 2 with details omitted for convenience. The graining table 85 comprises basically a working surface 86 joined to longitudinal side walls 87 and transverse side walls 88 which together completely border the working surface 86. The feeding means for supplying the strip of metal sheet 25 to the graining table 85 and the recovery means for withdrawing the metal sheet 25 from the graining table 85 are not illustrated in FIG. 6 and arrangements analogous to the feeder roll 34 and collector roll 59 of FIG. 2 may be suitably employed.

The principal distinction between graining table 85 of FIG. 6 and the graining table 27 of FIG. 2 both used in practicing the process of this invention is that the graining table 85 is stationary, that is, it is supported by legs 89 without any intermediate spring mounts. Moreover, the table 85 does not have any associated oscillating means such as the oscillator 30 as shown in FIG. 2 to vibrate the working surface 86. The oscillatory motion necessary to achieve the desired graining for the graining table 85 of FIG. 6 is imparted or transmitted to the metal balls 12 on the Working surface 86 by utilizing the caging means 90. The caging means 90 which are spaced above the working surface 86 and freely movable thereover basically comprise a cage 91 which is of generally rectangular configuration with vertical, continuous side walls 92 joined to and downwardly depending from a horizontal top 93. The top 93 and side walls 92 together define a bottom opening space 94 internal the cage 91 which is adapted to confine a plurality of the metal balls 12 on the working surface 86. The top 93 of the cage 91 is suspended from a rod 95 which connects to oscillator 96 of conventional design and capable of producing rotary motion over a controllable range of revolutions per minute. The oscillatory motion created by the oscillator 96 is transmitted to the cage 91 via the rod 95 and a corresponding vibration is thereby induced to the graining balls 12 confined within the cage 91 by an impulse contacting of the metal balls 12 generally against the side walls 92 and if desired, also against the top 93.

The cage 91 is constructed so that its dimension transverse to the graining table 85 is substantially equivalent to the width of the metal sheet 25 and is adapted so that a sufficient number of the metal graining balls 12 are confined within the internal space 94 of the cage 91 to substantially cover in one layer the surface of the metal sheet passing below the cage. As the strip of metal sheet 25 passes over the working surface 86, it travels beneath the oscillating cage 91. This allows the metal balls 12 confined within the cage 91 to contact, with agitated, rotary motion, the upper surface of the strip of metal sheet 25 in the presence of the particulate abrasive (not shown) such as sand present on the working surface 86 usually in aqueous slurry which thereby achieves the desired graining. The abrasive is supplied to the graining table 85 in a manner similar to the abrasive delivery for the table 27 of FIG. 2 such as by delivering abrasive via feed pipe 31 and withdrawing spent abrasive via a drain pipe 32 both of which are not shown in FIG. 6 for convenience.

The oscillator 96 to which the rod 95 is connected may be suitably mounted on an overhead frame 97 and any number of the cages 91 having a rod 95 and an oscillator 96 may be suspended along the frame 97. The particular number of cages 91 will, in any instance, be selected so that the desired graining is achieved in one pass of the strip of metal sheet 25 over the graining table 85. For convenience and simplicity, only two cages 91 and 91a are illustrated for the graining table 85. As with table 27 of FIG. 2, guides 98 are provided on the working surface 86 along the traveling path of the metal sheet 25 to bias the lower surface of the metal sheet flushly against the working surface 86 and additionally for table 85 to insure that the metal sheet 25 passes directly below each cage 91. Again, suitable guides 98 include a transversely disposed rod 99 spaced above the working surface 86 and supported thereon by brackets 100. In general, any number of the guides 98 can be disposed along the path of the traveling metal sheet 25 and in a preferred arrangement at least one guide 98 is positioned immediately before and after each of the cages 91.

I claim:

1. A continuous process for the graining of metal sheet which comprises continuously charging a strip of the metal sheet to a graining zone, contacting the metal sheet therein with agitated particles in the presence of a particulate abrasive, continuously charging fresh abrasive to the graining zone and withdrawing spent abrasive therefrom, maintaining the metal sheet within the graining zone for a period of time sufficient to roughen at least its upper surface by action of the abrasive and thereafter continuously recovering the surface roughened strip of metal sheet from the graining zone.

2. The process of claim 1 wherein the roughened metal sheet from the graining zone is first passed through a washing zone prior to recovery and is contacted therein with water to remove adhering abrasive.

3. The process of claim 1 wherein the strip of metal sheet prior to being charged to the graining zone is passed through a degreasing zone to remove surface contamination.

4. The process of claim 1 wherein the agitated particles are metal graining balls having a diameter of from about 0.25 to about 0.5 inches and have an imparted oscillatory movement equivalent to from about 50 to about 250 revolutions per minute.

5. The process of claim 1 wherein theparticulate abrasive is present in an aqueous slurry.

he process of claim 5 wherein the particulate abrasive has a diameter average ranging from about 50 to about microns.

7. The process of claim 5 wherein the abrasive slurry contains a metal cleaner.

8. The process of claim 1 wherein the particulate abrasive is continuously charged and withdrawn from the graining zone at a rate equivalent to from about 0.15 to 1.0 pounds of abrasive per minute per square foot of metal sheet being grained.

9. The process according to claim 1 wherein the particulate abrasive is charged and withdrawn from the graining zone in countercurrent flow to the direction of the strip of metal sheet.

10. The process of claim 1 wherein the strip of metal 

1. A continuous process for the graining of metal sheet which comprises continuously charging a strip of the metal sheet to a graining zone, contacting the metal sheet therein with agitated particles in the presence of a particulate abrasive, continuously charging fresh abrasive to the graining zone and withdrawing spent abrasive therefrom, maintaining the metal sheet within the graining zone for a period of time sufficient to roughen at least its upper surface by action of the abrasive and thereafter continuously recovering the surface roughened strip of metal sheet from the graining zone.
 2. The process of claim 1 wherein the roughened metal sheet from the graining zone is first passed through a washing zone prior to recovery and is contacted therein with water to remove adhering abrasive.
 3. The process of claim 1 wherein the strip of metal sheet prior to being charged to the graining zone is passed through a degreasing zone to remove surface contamination.
 4. The process of claim 1 wherein the agitated particles are metal graining balls having a diameter of from about 0.25 to about 0.5 inches and have an imparted oscillatory movement equivalent to from about 50 to about 250 revolutions per minute.
 5. The process of claim 1 wherein the particulate abrasive is present in an aqueous slurry.
 6. The process of claim 5 wherein the particulate abrasive has a diameter average ranging from about 50 to about 175 microns.
 7. The process of claim 5 wherein the abrasive slurry contains a metal cleaner.
 8. The process of claim 1 wherein the particulate abrasive is continuously charged and withdrawn from the graining zone at a rate equivalent to from about 0.15 to 1.0 pounds of abrasive per minute per square foot of metal sheet being grained.
 9. The process according to claim 1 wherein the particulate abrasive is charged and withdrawn from the graining zone in countercurrent flow to the direction of the strip of metal sheet.
 10. The process of claim 1 wherein the strip of metal sheet is maintained within the graining zone for a period sufficient to produce a grained metal sheet having a wetability angle with distilled water of from about 0* to about 30*.
 11. The process of claim 1 wherein the strip of metal sheet is composed of aluminum.
 12. The process of claim 1 wherein the particulate abrasive is selected from the group consisting of sand, pumice, marble and quartz. 